Use the search function. There are 19 threads about it going back to 2007.

Edit: In case it isn't clear from the website, MaXX is just a replacement for the Indigo Magic Desktop. It certainly doesn't emulate Irix in any way shape or form, although it was encumbered by some SGI intellectual property until recently—I don't know if that has changed. The SGI license required that it only be distributed for the RedHat platform.

MaXX is just a desktop environment (DE) for Linux designed to look and work like IRIX's IRIX Interactive Desktop (IID). It's releases are named after SGI products, the way Mac OS releases used to be named after cats. The first one was named Origin, the latest is Indy, and the releases coming out next year will be named Indigo, O2, etc. It's just a name, not emulation of said system. MaXX does not, at the moment, run IRIX software, and would require emulation of the MIPS processor as well as numerous system elements to do so. If we ever do see IRIX apps running on MaXX, it will first require emulation of one of SGI's platforms (likely IP22, used by the Indy and Indigo2, or IP32, used by the O2 and O2+), which will likely run inside MAME, GXEmul, or some other emulator. Again, this requires emulation of not just the MIPS CPU (say an R4400), but also of the entire system (SCSI disk controller, ethernet controller, VINO video hardware, Newport graphics, and motherboard stuff like the Dallas Semiconductor PROM chip, in the case of the Indy). So far, the farthest anything seems to have gotten is GXEmul's IP32 mode being able to boot an O2 PROM image dumped over serial if an older version of GXEmul is used, and show the system maintenance menu, but even it's limited (for example, graphics are seemingly only a framebuffer, so you don't get any of the features of the O2's CRM chipset).